Motor control device

ABSTRACT

A technique for smoothly speed-controlling a speed of a motor whose time constant is relatively small, such as a supersonic motor, under a relatively rough speed control profile and a simple configuration is disclosed. According to this technique, a frequency division number calculating section  1  changes a division number A under the relatively rough speed control profile and sets for a frequency division number setting register  2 . The comparator  3  outputs a+count signal if the division number A set by the frequency division number calculating section is greater than a current division number B counted by a frequency division number counter  4  (the division number A&gt; the division number B), and outputs a—count signal if the division number A&lt; the division number B. The frequency division number counter performs a+count on an enable clock of a time width t, which is shorter than the speed control profile of the frequency division number calculating section, if the+count signal is applied from the comparator, and performs a—count if the—count signal is applied from the comparator, and consequently counts the current division number B of a frequency divider  5  and applies this to the frequency divider.

TECHNICAL FIELD

The present invention relates to a motor control apparatus forperforming an acceleration control and a deceleration control on a motorwhose time constant is relatively small, such as a supersonic motor, inaccordance with a speed control profile.

BACKGROUND ART

Typically, when a rotation speed of a motor is controlled from a stopstate to a final target speed under a constant acceleration, a speedcontrol is carried out in accordance with a speed control profile inwhich a specification speed is increased in a stepped manner from 0 tothe final target speed. Also, a supersonic motor is further deceleratedas a drive frequency becomes higher, and further accelerated as thedrive frequency becomes lower. Thus, when the rotation speed of thesupersonic motor is controlled from the stop state to the final targetspeed under the constant acceleration, as shown in FIG. 3A, it iscontrolled in accordance with the speed control profile in which thedrive frequency that is the specification speed is decreased in thestepped manner. Here, a waveform a shown in FIG. 3A indicates the speedcontrol profile when the acceleration control is executed such that thedrive frequency is decreased by 2 kHz for each predetermined time width=0.5 sec by dividing into five stages from a stop drive frequency =72kHz to a final drive frequency =62 kHz.

FIG. 4 shows the conventional example of carrying out the control inaccordance with the speed control profile shown in FIG. 3A, and this isprovided with a frequency division number calculating section 1 and afrequency divider 5. The frequency division number calculating section 1is constituted by software of CPU and counts the pulses fed back from anencoder installed in the supersonic motor, changes a division number Aof the frequency divider 5 in accordance with the speed control profileshown in FIG. 3A, and sets for the frequency divider 5. The frequencydivider 5 divides a standard clock at a division ratio=1/A correspondingto the division number A set by the frequency division numbercalculating section 1, and applies as a drive pulse to the supersonicmotor. Also, as the other conventional examples, they are disclosed inthe following patent documents 1, 2 and the like.

Patent Document 1: Japanese Laid Open Patent Application (JP-A-Heisei,9-261979)

Patent Document 2: Japanese Laid Open Patent Application (JP-A-Heisei,9-247966)

However, in the case of the motor whose time constant is relativelysmall such as the supersonic motor, when the control for theacceleration and deceleration is carried out in accordance with thespeed control profile of the stepped manner, the actual speed of themotor is not smoothly accelerated and decelerated because it follows thespeed control profile of the stepped manner. So, in the motor whose timeconstant is relatively small, in order to attain the smooth accelerationand deceleration, as indicated in a waveform β of FIG. 3B, the speedcontrol profile of the stepped manner needs to be finely set. Thus, whenthe control is carried out by setting the target speed through thesoftware of the CPU, an expensive speed control system whose processingspeed is fast is required. Here, the waveform β shown in FIG. 3Bindicates the speed control profile when the acceleration control iscarried out by dividing the predetermined time width=0.5 sec shown inFIG. 3A for each 0.1 sec and decreasing it by 2 kHz/5=0.4 kHz for each0.1 sec. Also, for example, in the techniques of the patent documents 1,2, there is a problem that a complex system is required.

DISCLOSURE OF THE INVENTION

The present invention is proposed in view of the above-mentionedproblems in the conventional examples and has an object to provide amotor control apparatus, which can smoothly perform a speed control on aspeed of a motor whose time constant is relatively small, such as asupersonic motor, under a relatively rough speed control profile and asimple configuration.

In order to attain the above-mentioned object, the present invention isconfigured so as to have:

dividing means for dividing a standard frequency and generating a drivesignal of a motor;

division ratio calculating means for calculating and outputting adivision ratio of the dividing means in accordance with a speed controlprofile of the motor; and

division ratio converting means for converting the division ratiooutputted by the division ratio calculating means so as to obtain aspeed control profile finer than the speed control profile and settingfor the dividing means.

With the above-mentioned configuration, only by adding the divisionratio converting means for dividing in accordance with the speed controlprofile finer than the speed control profile of the division ratiocalculating means and setting for the dividing means, it is possible tosmoothly speed-control the speed of the motor whose time constant isrelatively small, such as the supersonic motor, under the simpleconfiguration, even if the speed control profile of the division ratiocalculating means is rough.

Also, the division ratio calculating means calculates and outputs adivision number of the dividing means in accordance with the speedcontrol profile, and

the division ratio converting means counts up or counts down a clock,which is shorter than a time width of the speed control profile of thedivision ratio calculating means, on the basis of the division numberoutputted by the division ratio calculating means, and sets for thedividing means.

Also, the motor is characterized in that it is the supersonic motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an embodiment of a motor controlapparatus according to the present invention;

FIG. 2 is an explanation view showing a main signal of the motor controlapparatus of FIG. 1;

FIG. 3A is an entire view showing a speed control profile;

FIG. 3B is a partial detailed view showing the speed control profile;and

FIG. 4 is a block diagram showing an embodiment of a conventional motorcontrol apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below withreference to the drawings. FIG. 1 is a block diagram showing theembodiment of a motor control apparatus according to the presentinvention, and FIG. 2 is an explanation view showing a main signal ofthe motor control apparatus of FIG. 1.

In FIG. 1, the same reference symbols are given to the same devices asthe configuration explained in the conventional example (the frequencydivision number calculating section 1 and the frequency divider 5). Thefrequency division number calculating section 1 is constituted by thesoftware of the CPU, and counts the pulses fed back from the encoderinstalled in the supersonic motor (not shown) and also inputs (reads) acurrent division number B of the frequency divider 5 counted by afrequency division number counter 4 and consequently converts thedivision number B into the division number A, in accordance with arelatively rough speed control profile, for example, as shown in FIG.3A, and then sets for a frequency division number setting register 2.The division number A set for the frequency division number settingregister 2 is inputted to an input terminal a of a comparator 3.

The comparator 3 outputs a+count signal if the division number A> thedivision number B, namely, if the division number A set by the frequencydivision number calculating section 1 is greater than the currentdivision number B counted by the frequency division number counter 4,and on the other hand, outputs a—count signal if the division number A<the division number B. The frequency division number counter 4 performsa+count (count-up) on an enable clock of a time width t, which isshorter than the relatively rough speed control profile shown in FIG.3A, if the +count signal is applied from the comparator 3, and performsa—count (count-down) if the—count signal is applied from the comparator3, and consequently counts the current division number B of thefrequency divider 5, and applies this to the frequency divider 5 (and aninput terminal b of the comparator 3 and the frequency division numbercalculating section 1).

Here, the supersonic motor is further accelerated as the drive frequencybecomes lower. Thus, when the rotation speed of the supersonic motor iscontrolled from the stop state to the final target speed under theconstant acceleration, it is controlled in accordance with the profilein which the drive frequency becomes lower in the stepped manner. Hence,since the frequency division number calculating section 1 increases thedivision number A, the comparator 3 outputs the +count signal to thefrequency division number counter 4. The frequency division numbercounter 4 performs the +count on the enable clock and increases thecurrent division number B of the frequency divider 5 for each enableclock. Consequently, the division number B corresponding to the profilefiner than the relatively rough profile shown in FIG. 3A is set for thefrequency divider 5.

Here, FIG. 2 shows a profile different from the speed profiles shown inFIG. 3A and FIG. 3B. The frequency division number calculating section 1increases the division number A to 2590 from 2570 of the same value asthe division number B, in order to carry out the acceleration bydecreasing the drive frequency of the supersonic motor from 70 kHz to69.5 kHz. The comparator 3 outputs the +count signal because thedivision number A> the division number B. The frequency division numbercounter 4 performs the +count on the enable clock of the time widthwhich is finer than the speed control profile of the division number A,and the division number B of the frequency divider 5 is increased foreach count. When a standard frequency of the frequency divider 5 isassumed to be 180 MHz, the followings are obtained.70 kHz≈180 MHz/257069.5 kHz≈180 MHz/2590

Thus, on the basis of the time width t of the enable clock and the countunit of the frequency division number counter 4, the drive frequency ofthe supersonic motor can be speed-controlled finer than the speedcontrol profile of the frequency division number calculating section 1.Hence, the speed of the motor whose time constant is relatively small,such as the supersonic motor, can be smoothly speed-controlled inaccordance with the relatively rough speed control profile and thesimple configuration.

INDUSTRIAL APPLICABILITY

As mentioned above, according to the present invention, it is possibleto provide the motor control apparatus which can smoothly speed-controlthe speed of the motor whose time constant is relatively small, such asthe supersonic motor, under the simple configuration, even if the speedcontrol profile is rough.

1. A motor control apparatus having: dividing means for dividing astandard frequency and generating a drive signal of a motor; divisionratio calculating means for calculating and outputting a division ratioof said dividing means in accordance with a speed control profile ofsaid motor; and division ratio converting means for converting thedivision ratio outputted by said division ratio calculating means so asto obtain a speed control profile finer than said speed control profileand setting for said dividing means.
 2. The motor control apparatusaccording to claim 1, wherein said division ratio calculating meanscalculates and outputs a division number of said dividing means inaccordance with said speed control profile, and said division ratioconverting means counts up or counts down a clock, which is shorter thana time width of said speed control profile of said division ratiocalculating means, on the basis of the division number outputted by saiddivision ratio calculating means, and sets for said dividing means. 3.The motor control apparatus according to claim 1 or 2, wherein saidmotor is a supersonic motor.